| oligoclase |
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noun
- (mineralogy) A plagioclase feldspar, the second member of the Albite-Anorthite solid solution series. Primarily found as small crystals in impure marble. Oligoclase contains a small amount of calcium substituting for some of the sodium in its formula. Oligoclase with reddish-golden inclusions found in Norway and Canada is called sunstone.
- Chemical composition: Sodium calcium aluminum silicate, <math>Na_xCa_xAlSi_3O_8</math>
- Physical properties:
Moh's Hardness: 6.0
Specific gravity: 2.65
Color: white, yellow, reddish-gray
Luster: glassy
Fracture: conchoidal
Cleavage: two good at about 94º to each other
- Habit: Triclinic - pinacoidal. Usually twinned and striated, but this may not be visible to the unaided eye.
| | | olivine |
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noun
- (mineralogy) any of a group of olive green magnesium-iron silicate minerals that crystallize in the orthorhombic system
| | omphacite |
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noun - (mineralogy) any of a range of green, monoclinic pyroxene minerals found in eclogites and similar rocks; they are solid solutions of jadeite and diopside
| | Opal |
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proper noun
- (given name, female) from the precious stone, invented in the nineteenth century.
- A type of petrol made by the BP company designed to be unable to used for petrol sniffing. (Reference: BP article on Opal http://www.bp.com/sectiongenericarticle.do?categoryId=9008933&contentId=7016884.)
| | ore |
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noun
- rock, Rock that contains enough of one or more metals to be worth processing to obtain the pure metal or metals. Ore usually comes from a mine.
| | orpiment |
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noun (uncountable)
- arsenic trisulphide, occuring naturally in crystals or massive deposits, formerly used as a dye or pigment
| | orthoclase |
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noun
- (mineralogy) A common feldspar of igneous, plutonic, and metamorphic rocks. Orthoclase is the main feldspar of pegmatite occurrences, where it is most commonly flesh-colored. Orthoclase is used in the ceramic and glass industries and as a decorative gravel.
- Chemical composition: Potassium aluminum silicate, <math>KAlSi?_3O_8</math>
- Physical properties:
Moh's Hardness: 6.0
Specific gravity: 2.6
Color: white, flesh, yellow, brown, occasionally colorless
Luster: glassy
Fracture: conchoidal
Cleavage: two good at 90º
- Habit: Monoclinic - prismatic. Well developed crystal faces are at 90º to each other. Occasional twinned crystals are found. Crystal faces typically look polished, and are not striated.
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